The present invention generally relates to a high frequency heating apparatus, and more particularly to a high frequency heating apparatus for cooking or a microwave oven of a type which includes an oven defining structure having an access opening leading into a heating chamber in the oven defining structure, a drawer type door assembly for selectively closing and opening the access opening, a support shelf member fixed to the door assembly in a cantilever state, and a turn-table mounted on the support shelf member and operated by magnetic coupling through remote driving from the outside of the heating chamber during the heating of an object to be heated or cooked.
Generally, in a high frequency heating apparatus which is arranged to heat objects such as food material, the heating is based on the principle of dielectric heating. The object is cooked by the generation of heat at the interior of said object which is different from the heating by electric heaters or the like wherein the object is heated from the exterior thereof, and therefore, in the presence of uneven heating, there has been a possibility that the interior of the object to be heated is cooked excessively, while the exterior thereof appears not done, thus resulting in a failure of the electric heaters or the like to cook effectively.
For preventing uneven heating as described above, various conventional arrangements have been proposed in which the rotation of the object to be heated, which is mounted on a turn-table during cooking is often employed as one method of achieving stable heating. In the above cases, an arrangement in which a turn-table is driven by a magnetic coupling through remote control from outside of the heating chamber is considered to be extremely convenient for practical use from the viewpoint of cleaning, etc. the interior of the heating chamber. Additionally, when the heating apparatus is used while in a low position, for example, in a state where it is directly placed on a floor or the like, it is recommended for convenience of operation to employ a heating apparatus of a type in which the door assembly is arranged to reciprocate in the direction of the depth of the apparatus for the selective closing and opening of an access opening, and the support shelf for the turn-table is mounted at its one edge to the door assembly and is inserted into or withdrawn from the heating chamber following a closing or opening of said door assembly.
Incidentally, for meeting the requirements of construction as described above in which the turn-table is driven through an external remote driving with the turn-table and the support shelf therefor being arranged to be inserted or withdrawn into the heating chamber respectively as the door assembly is moved for closing and opening, there are serious problems which are related to a stable holding of the support shelf in position. More specifically, when the support shelf is intended to be held in position only at its one edge by the door assembly alone, the height and inclination of the turn-table may be undesirably altered due to a bending or warping thereof upon the placing of an item to be heated on the turn-table, thus resulting in a hindrance of the smooth remote driving of the turn-table through the magnetic coupling. While on the contrary, if it is so arranged that the support shelf is supported at its opposite edges, with the one edge thereof being held by the door assembly and rollers or the like provided at its other edge and being adapted to contact the bottom wall of the heating chamber at all times, the depth or length of the support shelf is required to be larger than a stroke or distance necessary for the movement of the door assembly for the closing and opening thereof, thus the depth of the heating chamber is undesirably increased. However, when it is attempted to take out the object to be heated or a receptacle therefor from the heating chamber having a door assembly of drawer type, it is rather difficult unless the object to be heated or the receptacle is considerably smaller than the stroke for opening and closing the door assembly. Therefore, it is inconvenient that the depth of the heating chamber is longer than the stroke for opening or closing the door assembly.
Accordingly, in a high frequency heating apparatus having a turn-table, driven through remote control from the exterior of the heating chamber, and the support shelf therefor which are arranged to be inserted or withdrawn with respect to the heating chamber following movement of the door assembly in the direction of depth of the heating chamber for closing and opening, it is considered very significant to arrange the apparatus so that the stroke for opening and closing the door assembly thereof may be set as desired irrespective of the depth of the heating chamber, and that during driving of the turn-table thereof, the positional relation between the turn-table and the bottom surface of the heating chamber is correctly maintained.